It is well known from the technical literature, including patents, that olefins can be effectively oxidized with osmium compounds, particularly osmium tetroxide, to their corresponding diols when the reaction is carried out with catalytic amounts of osmium tetroxide and a stoichiometric amount of a strong co-oxidizing agent. The oxidizing agents which have been proposed and used include the alkali metal chlorates and hypochlorites, potassium ferrocyanide and hydrogen peroxide (see U.S. Pat. Nos. 2,414,385 and 2,773,101, which use hydrogen peroxide with the latter teaching that inorganic peroxides, such as sodium and barium peroxides, or organic peroxides, such as tertiary butyl peroxide, tertiary butyl hydroperoxide, or benzoyl peroxide, can be used instead of the hydrogen peroxide).
Oxidation of Os.sup.+6 to Os.sup.+8 with molecular oxygen in aqueous alkaline solutions has also been reported, thus under these conditions olefins are oxidized to their corresponding diols at a pH in the range of 8.5-10.5 and to oxalic acid at a pH of 12.5. The reaction rate is slow, however, and the reaction ceases when the molar ratio of diol to osmium tetroxide exceeds 2. (See U.S. Pat. No. 4,049,724).
U.S. Pat. No. 4,049,724 improves the hydroxylation of olefins by homogeneous catalyzation relying on an aqueous solution of an organic hydroperoxide, e.g. t-butyl hydroperoxide, maintained at a pH of 8 to 12 by the presence of an appropriate amount of base, e.g., sodium carbonate. Low yields were reported and control of pH is necessary. This confirms the teaching of K. B. Sharpless in JACS, Mar. 31, 1976, pp. 1986-7 that whereas alkaline solutions of hydrogen peroxide decomposed violently in presence of OsO.sub.4, solutions of t-butyl hydroperoxide in the presence of base (tetraethylammonium hydroxide gave yields superior to that obtained with sodium or potassium hydroxide) and OsO.sub.4 were stable and provided good yields of vicinal diols from a variety of olefins.
Recently, U.S. Pat. No. 4,203,926 has taught the heterogeneous catalysis of ethylene and propylene to the corresponding glycol in a process in which ethylbenzene hydroperoxide is reacted with the olefin in a two-phase liquid (organic-aqueous) reaction system in the presence of osmium tetroxide and cesium, rubidium or potassium hydroxide. This two-phase system requires organic soluble hydroperoxides and appears specific for ethylbenzene hydroperoxide.
It is therefore an object of this invention to provide a new homogeneous catalysis method for the hydroxylation of olefins to generate valuable glycols.